Line of sight (LOS) systems are commonly used in targeting applications. Some typical technological implementations for LOS systems are electromagnetic (EM), optical, inertial and acoustic.
Generally, prior art EM LOS systems comprise a three-axis magnetic dipolar radiator and a three-axis magnetic dipolar sensor, which are located in a metallic surrounding, such as an airplane cockpit, a tank, or any other type of vehicle. The sensor is typically located on or near a mobile element within a restricted motion box, such as on a helmet or a crew member's seat, and the radiator is typically rigidly installed in the general area.
When the EM LOS system is activated, an EM field is generated in the area of the radiator. Utilizing known in the art electromagnetic principles and mathematical principles, it is possible to generate a model representative of the EM field, and to determine therefrom the position and orientation (P & O) of the sensor. Knowing the sensor position and orientation is very useful since this also provides information for targeting direction.
Unfortunately, the metallic parts in the surrounding react to magnetic fields, causing distortions in the electromagnetic field. Thus, since each individual vehicle has its own unique EM field, without appropriate calibrations the resultant P & O estimations may not be accurate enough for targeting purposes. In order to produce more accurate P & O estimations, common practice is to map the motion box magnetic field, estimate the EM field model, and store the mapped model coefficients in the EM LOS systems firm ware. The stored model is then used when estimating the real time P & O.
Since over the course of time mechanical installation of radiators, the electrical parameters, sensor calibrations, and so on, tend to drift, and since cockpit parts may change position slightly, the mapped magnetic model must typically be updated on a regular basis, such as annually. However, unfortunately, variations which may occur in the magnetic field between mappings are not compensated for. As such, the resultant calculations may be less accurate than desired.
One solution is to perform mapping on a more regular basis, such as weekly. Unfortunately, this is not a feasible endeavor. In order to map, the vehicle must be grounded, and mapping takes time and is expensive. Thus, there exists a need for methods and apparatus to which avoid expensive mapping of each vehicle in the fleet, that adapts to the small drifts in the EM field—regardless of the source of drift, and produces more accurate position and orientation estimations.